CYTOKINE INTERACTIONS IN HUMAN MIXED LYMPHOCYTE CULTURE

Human PBMC of healthy blood donors were used to investigate the intera ction of cytokines in human MLC. Two-way MLC was performed because irr adiation did not influence the cytokine release. We found different ki netic patterns for IL-2, IFN-gamma, and sIL-2R. Production of IFN-gamm a was dependent on IL-2 release because anti-IL-2 addition resulted in more than 90% reduced IFN-gamma levels. Treatment with rIL-2 altered IFN-gamma kinetics, but not the total amount of IFN-gamma. Addition of anti-IFN-gamma led to decreased production of IL-2 and sIL-2R. A down -regulation of IL-2 and sIL-2R could also be observed after treatment with rIFN-gamma. No production of IL-4 and IL-10 was detected in MLC ( detection limit 5 pg/ml). This could not be explained by IFN-gamma ant agonism because IL-4 and IL-10 were not detectable even after addition of anti-IFN-gamma. Testing the TH1- TH2 cell antagonism, the addition of rIL-4 and rIL-10 resulted in IFN-gamma suppression depending on th e timing of exposition. Treatment with rIL-10 inhibited IL-2 and sIL-2 R release. We found no production of IL-1 alpha and IL-1 beta in MLC, whereas IL-6 and TNF-alpha release could be detected. Surprisingly, re lease of IL-6 and TNF-alpha could be blocked completely by addition of anti-IFN-gamma. This suggests that the release of IL-6 and TNF-alpha in MLC is dependent on IFN-gamma produced by T cells. In summary, TH1 cytokines play a central role in MLC regulation, whereas TH2 cytokines appear to be of little importance.